The invention relates to irrigation means for the uniform distribution of a controlled quantity of liquid and preferably installed under the surface of the ground.
Known irrigation systems in essence work on one of the following principles. In one system, tubes are used having a small diameter and pore-like outlet apertures giving small outlet quantities. The small outlet quantities result in a small liquid pressure drop. The small outlet quantities are occasioned by the tiny outlet apertures and the largest possible wall thickness of the tube. This means that the wall thickness is often thicker than might be necessary for production reasons and that the pore-like outlet apertures can very rapidly become blocked by impurities that are carried along in the liquid, whereby the irrigation system soon becomes useless. This disadvantageous result can be delayed only by means of expensive filtering plant.
In another system, tubes are used having a large diameter and individual outlet apertures giving large outlet quantities. A large liquid pressure drop occurs along the tube by reason of the large outlet quantities. The large pressure drop results in markedly different outlet quantities at the individual outlet apertures. Consequently, only short tube lengths can be used in order that the different outlet quantities at the individual outlet apertures and the resultant non-uniform liquid distribution can be kept within acceptable limits. However, short tube lengths require a larger number of inlet points. The installation costs are therefore very high and the system is uneconomical for many purposes.
According to a third known irrigating method, the tubes are equipped with individual adjustable outlet valves. Setting of the individual valves achieves the desired uniformity in the distribution of liquid along the tube. However, this method is very uneconomical because of the high manufacturing costs and the labour time for setting the individual valves.